This application claims the benefit of priority under 35 U.S.C. xc2xa7 119 of Japanese Patent Application No. H11-273064, filed on Sep. 27, 1999.
1. Field of the Invention
This invention relates to an ATM (asynchronous transfer mode) switch, and more particularly, to an ATM switch suitable for realizing a connectionless communication system in an ATM network.
2. Description of the Related Art
An ATM network using an ATM switch is a connection-oriented network. That is, An ATM switch is a network configured to previously set a virtual connection (line) for communication.
Therefore, in an ATM network, even when a communication of a type not previously setting a virtual connection is used, it is necessary to set a virtual connection (line) therefore, and a large number of lines must be set. A typical example of communication not previously setting a virtual connection (line) is IP (Internet Protocol) communication.
However, as users of an ATM communication network increase, virtual connections (lines) also increase. Since specification of ATM switches is fixed assuming that virtual connections (lines) are set and released whenever necessary, when a large number of virtual connections (lines) are set in an ATM network, the address space for identifying virtual connections may come to be insufficient for accommodating connectionless communications.
In order to prevent that an enormous number of virtual connections are set in an ATM network, conventional ATM communication networks relied on merger of virtual connections using SAR (segmentation and reassembly) devices for transmission of ATM cells, which are packet-format.
More specifically, as shown in FIG. 20, a packet 100 dealt with in an upper layer protocol of ATM networks, such as IP communication, for example, is divided into a plurality of ATM cells 110 of 53 bytes when transmitted on an ATM network. When a plurality of virtual connections are merged, it must be ensured that divisional ATM cells 110 of the packet 100 do not mix up and can be reproduced into the packet 100 at the terminal device (node) of a destination.
Conventional ATM switches, however, did not have the function of merging virtual connections, and relied on the use of a SAR device as a logical terminal point of a virtual connection (line) to merge virtual connections.
This SAR device was located outside an ATM network, and configured to reconstruct ATM cells of a packet sent by different virtual connections thereby to merge the virtual connection, and thereafter send them again as ATM cells to the ATM communication network by using the SAR device.
This system, however, involved the problem that the communication capacity of virtual connections that could be merged was limited by the processing capability of the SAR device, and the ATM switch could not sufficiently perform its own switching capacity.
Moreover, such a SAR device also had certain functions other than the function of stockpiling and switching packets. However, since the function required for merging virtual connections was only the function of stockpiling and switching these packets, it was not necessary to use the SAR device. That is, the use of a SAR device was fruitless in the specification of the ATM switch.
It is therefore an object of the invention to provide an ATM switch having the function of merging of virtual connections. Accordingly, it is another object of the invention to relax restrictions on the switching performance caused by the use of a SAR device and ensure sufficient performance of the switching ability an ATM network originally has.
In order to accomplish the aforementioned and other objects, according to one aspect of the present invention, an ATM switch transmitting ATM cells arrived through a plurality of different virtual connections by merging them into a single virtual connection, comprising:
virtual connection queues which store the ATM cells classified according to the individual virtual connections;
one or more packet queues which store an identifier of the virtual connection used for the transmission of the ATM cells for forming a packet, when a final ATM cell of the packet arrives; and
a scheduler configured to scan the packet queues, extract one identifier from the packet queue storing the identifiers, select one of the virtual connection queues to be next transmitted in accordance with the identifier extracted from the packet queue, and successively transmit ATM cells in a unit of packet from the virtual connection queue selected.
According to another aspect of the present invention, a control method of an ATM switch transmitting ATM cells, comprising the steps of:
classifying and storing the ATM cells in virtual connection queues according to virtual connections through which the ATM cells are arrived;
storing an identifier of the virtual connection used for transmission of the ATM cells for forming a packet in one or more packet queues, when a final ATM cell of the packet arrives; and
scanning the packet queues, selecting one of the virtual connection queues to be next transmitted in accordance with a storing order of the identifier in the packet queues, and successively transmitting ATM cells in a unit of packet from the virtual connection queue selected to another virtual connection.